Chickpea Varieties Reveal Metabolic Secrets of Zinc Tolerance

Zinc is one of those nutrients that plants cannot live without, yet too much of it can quietly poison them. In agricultural regions where soils are contaminated by industrial activity, mining, or over-application of fertilizers, the line between essential micronutrient and toxic burden becomes dangerously thin. Chickpea, one of the world’s most important legume crops and a cornerstone of protein security across South Asia, the Middle East, and beyond, is particularly vulnerable to this balancing act. Now, a team of researchers has taken one of the most detailed looks yet at how different chickpea varieties cope with excess zinc, combining classic growth measurements, physiological assays, biochemical profiling, and cutting-edge metabolomics to reveal what separates the resilient from the fragile.

The study, led by Shakir Ullah and colleagues working at Northeast Forestry University in Harbin, China, in collaboration with Ahmed A. Elateeq of Al-Azhar University in Egypt, examined three chickpea varieties: ICCV89310 (abbreviated IC8), NC234 (NC2), and ICCV89323-B (IC8-B). The researchers grew the plants in hydroponic culture under four zinc sulfate concentrations: a control treatment with no added zinc, and stressed treatments of 50, 100, and 150 micromolar. This controlled setup allowed the team to isolate the effects of zinc toxicity from the confounding factors of soil chemistry, while simultaneously tracking zinc uptake and distribution using inductively coupled plasma optical emission spectrometry, or ICP-OES, in both roots and shoots.

The findings were striking in their clarity. When exposed to rising zinc concentrations, the varieties IC8 and NC2 maintained robust growth, holding on to plant height, fresh weight, and dry weight far better than their counterpart. Their root-to-shoot ratios and relative shoot water content also held steadier, and they scored higher on the tolerance index, a measure of how well a plant sustains biomass under stress compared to unstated controls. By contrast, IC8-B faltered across virtually every metric, stunting visibly and losing physiological function as zinc levels climbed. The results establish IC8-B not simply as an underperformer but as a valuable scientific tool: a genuinely zinc-sensitive reference variety against which future chickpea lines can be benchmarked.

Beneath the visible differences in growth lay a deeper biochemical story. Excess zinc inside plant tissues disrupts photosynthesis, impairs water relations, and triggers the overproduction of reactive oxygen species, unstable molecules that attack membranes, proteins, and DNA. The team measured classic markers of this oxidative damage: hydrogen peroxide accumulation, malondialdehyde levels, and electrolyte leakage, which together reveal how badly cellular membranes have been compromised. In IC8-B, these stress markers surged, painting a picture of a plant overwhelmed by oxidative assault. In IC8 and NC2, the damage signatures were far milder, and the reason soon became clear in the activity of their antioxidant machinery.

The tolerant varieties mounted a coordinated antioxidant defense, with elevated activities of the key enzymes superoxide dismutase, peroxidase, catalase, and glutathione reductase, alongside higher levels of non-enzymatic protectants such as proline, soluble sugars, and total protein. Superoxide dismutase works as the first line of defense, converting superoxide radicals into hydrogen peroxide, which catalase and peroxidase then break down into water. Glutathione reductase keeps the cellular glutathione pool in its antioxidant form, sustaining the cycle. This enzymatic cascade, supported by osmoprotective compounds like proline that stabilize proteins and membranes under stress, gave IC8 and NC2 a decisive biochemical edge. The sensitive IC8-B simply could not keep its antioxidant systems running at the pace the stress demanded.

The most innovative portion of the study came from metabolomics. Using gas chromatography coupled with mass spectrometry, the researchers profiled the shoot metabolomes of all three varieties and quantified forty-six responsive metabolites spanning several chemical classes: organic acids, amino acids, amines, alcohols, and sugars. Among these, changes in histidine, asparagine, tryptophan, allantoin, and a suite of antioxidant-related metabolites stood out as hallmarks of the tolerant varieties. Histidine has long been implicated in metal chelation and internal metal transport, potentially binding excess zinc and keeping it away from sensitive metabolic sites. Allantoin, a purine metabolism byproduct increasingly recognized as a protective signaling molecule in plants, and tryptophan, the precursor of the growth-regulating auxin pathway, both shifted in patterns consistent with active stress management rather than passive decline.

These metabolic adjustments suggest that zinc tolerance in chickpea is not the product of a single heroic gene or enzyme, but of an orchestrated reallocation of primary metabolism. Amino acids serve double duty as osmolytes, chelators, and nitrogen reserves; sugars buffer cellular osmotic pressure and fuel energy-hungry repair processes; organic acids can complex metal ions in the vacuole, effectively locking them away. The tolerant varieties appear to have rewired these interconnected pathways to survive where the sensitive variety’s metabolism simply collapsed. Such integrated views, the authors argue, are essential for modern crop improvement, because tolerance traits selected on growth alone can mask the metabolic costs that determine long-term performance in contaminated fields.

The practical implications extend well beyond the laboratory. Zinc-contaminated soils are a growing global problem, and identifying germplasm that can maintain yield under such conditions is a priority for food security. IC8 and NC2 emerge from this work as promising candidates for cultivation in zinc-affected environments and as donor parents for breeding programs seeking to stack zinc tolerance alongside other stress-resilience traits. The multivariate analysis framework the team used, integrating growth, physiology, biochemistry, and metabolite profiles into a single comparative picture, also offers a template for screening other crops against other metal stresses, from cadmium to nickel. At the same time, the researchers are careful to note a critical caveat: their experiments were conducted in hydroponic culture, and field-scale confirmation remains necessary before any practical deployment. Soil chemistry, microbial communities, and climate can all modify metal availability in ways a nutrient solution cannot fully replicate.

Chickpea is grown on tens of millions of hectares worldwide and forms a dietary backbone for hundreds of millions of people, so even incremental gains in stress tolerance translate into significant food system benefits. By supplying both a tolerant germplasm set and a sensitive reference line, along with the metabolic fingerprints that explain the difference, this study hands breeders and physiologists a complete toolkit. It demonstrates that the answers to one of agriculture’s quieter crises may be written not in the visible architecture of the plant, but in the subtle chemistry of its amino acids, sugars, and acids, waiting to be read. The next step, moving these insights from hydroponic tanks into real soils, will determine whether this molecular understanding can finally reach the farmers who need it most.

Subject of Research: Zinc tolerance mechanisms in chickpea varieties under zinc sulfate stress

Article Title: Evaluation of chickpea (Cicer arietinum L.) varieties under ZnSO4 stress: Insights from growth, physiological, biochemical and metabolomics

Article References: Ullah, S., Li, X., Salam, U., Elateeq, A. A., Guo, X., & Tang, Z. (2026). Evaluation of chickpea (Cicer arietinum L.) varieties under ZnSO4 stress: Insights from growth, physiological, biochemical and metabolomics. The Science of Nature, 113(5), Article 105. https://doi.org/10.1007/s00114-026-02148-6

Image Credits: AI Generated

DOI: 10.1007/s00114-026-02148-6

Keywords: chickpea, zinc tolerance, ZnSO4 stress, oxidative stress, antioxidant defense, metabolomics, GC-MS, proline, allantoin, Cicer arietinum, heavy metal contamination, plant physiology